JPH0499201A - Stainless steel powder for sintering - Google Patents

Abstract

PURPOSE:To improve corrosion resistance and ground outer appearance in sintered parts by manufacturing a stainless steel powder for sintering containing O corresponding to the remaining C content in order to remove C in a remaining binder in a degreased body by oxidization-reduction. CONSTITUTION:O content to be contained in the stainless steel powder is decided with C content contained in the degreased body at the stage of degreasing an injection green compact. Further, this C content is decided with the degreasing condition. Therefore, the C content is beforehand obtd. by analyzing and based on this analyzed value, the necessary O content is obtd. by calculation and made to contain in the powder. By this method, C contained on the surface and in the inner part of the powder at the time of sintering, is removed and the sintered density is improved and also, inclusion and pin hole are remarkably reduced thereby sintered parts having excellent corrosion resistance and the ground outer appearance, can be obtd.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to the production of sintered crystals by injection molding of stainless steel powder, and particularly relates to stainless steel powder [Prior Art] Conventionally, organic binders have been blended with metal powder. A well-known method is to knead the mixture, injection mold it, degrease the resulting molded product, and then sinter it. Degreasing here is a process of removing the binder, and is generally performed by heat treatment. The atmosphere is even bigger next 2i! It can be divided into several parts.

b) Oxidizing atmosphere (Air etc)) Non-oxidizing atmosphere CNtAr etc) In b) In order to remove the binder, it is necessary to raise the heat treatment temperature until the binder thermally decomposes or burns, which causes the binder to come off. After degreasing, the powder in the degreased body is largely oxidized.

At the time of sintering, even if an attempt is made to remove O in the reaction of C+〇-CO, there is insufficient C to cover the amount of O, so O that is not reduced by C remains during sintering. One possibility is to leave the binder behind during degreasing, but it is extremely difficult to control this because the degreasing ends during thermal decomposition. Therefore, unreduced zero remains in the sintered body, causing inclusions and pinholes in the structure of the sintered body, resulting in problems such as low mechanical strength and reduced gloss on the polished surface.

In addition, in the atmosphere of (1), the powder in the degreased body after the binder is removed by thermal decomposition is hardly oxidized. However, since it is impossible to completely remove the binder, more C than necessary for reduction remains in the degreased body. Therefore, the obtained sintered body also contains a large amount of C, which causes problems such as deterioration of corrosion resistance and mechanical properties.

[Means to solve the problem]

The present invention was made to solve these problems, and its gist is to perform degreasing treatment in a non-oxidizing atmosphere,
In order to remove C in the binder remaining in the degreased body by redox reaction, stainless steel powder for sintering containing O in an amount corresponding to the amount of remaining C is prepared.

[Effect]

In the present invention, when a molded body of metal powder is sintered,
O contained in the powder causes a reaction of C+O-C◯, becomes a gas, and is removed from the metal powder. That is, the C contained in the degreased body and the O actively contained in the powder react with each other and are removed.

In addition, in the present invention, the amount of O that should be contained in the powder is
It is determined by the amount of C contained in the degreased injection molded article. Furthermore, the amount of C is determined by the degreasing conditions. Therefore, it is sufficient to analyze and determine the amount of C in advance, calculate the required amount based on the analysis value, and include it in the powder.

As described above, the present invention is characterized in that the powder is forcibly oxidized by heat treatment to incorporate O into the powder in order to remove C from the degreased body using the c+o-co reaction. Therefore, according to the present invention, C contained on the surface and inside of the powder is removed during sintering, improving the sintered density, and the number of inclusions and pinholes is significantly reduced, resulting in a good U-weave. Sintered parts with excellent corrosion resistance and polished appearance can be obtained.

〔Example〕

Next, in order to clarify the characteristics of the present invention, examples thereof will be described in detail below.

Example 1 5US-316 powder produced by water atomization with an average particle diameter of 10 μm and an oxygen content of 0.54 wt% was heated at 300° C. for 2 hours using an atmospheric furnace. Thereafter, analysis revealed that the oxygen content was 0.97 wt%.

To 100 parts by weight of this powder, 11.5 parts by weight of a binder containing polystyrene as a main component was added to perform crosstalk. After that, it was molded into 7 x 7 x by injection molding machine.
It was molded at a temperature of 165° C. in a mold having a cavity of 30 m to obtain a molded body of a test piece. The added binder was thermally decomposed by treating the obtained molded body in a debinding furnace. Of the binder added by this operation, 9
5.5% of the binder was stably removed. At this point, the amount of C was 0.61 wt%. Next, hydrogen was further introduced into the obtained degreased body in a vacuum atmosphere up to 1150°C, and sintered crystals were obtained by sintering at a maximum temperature of 1320°C for 8 hours.

As a result of analyzing the carbon content of the fired crystal, as shown in Table 1, O was as low as 0.0111°C%, and oxygen content was significantly reduced to 0.07 wt%.

When this baked crystal was tested for corrosion resistance, it showed good results, with no rusting in either the salt spray test or the artificial sweat test.

Example 2 5LIS-304 powder produced by water atomization with an average particle diameter of 9.2 μm and an oxygen content of 0.42 vt% was heat-treated at 300° C. for 2 hours using an atmospheric furnace.

Subsequent analysis revealed that the oxygen content was 0.89 wt%. To 100 parts by weight of this powder, 10.7 parts by weight of a binder containing acrylic as a main component was added. Thereafter, this was injection molded into a 4×3×40-mouth test piece mold at a temperature of 170° C. using an injection molding machine to obtain a molded body. By processing in the obtained degreasing furnace, 96.3% by weight of the binder among the added binders was stably removed. The amount of C at this point was 0.68 wt%. Next, the obtained degreased body is further introduced hydrogen in a vacuum atmosphere up to 1120°C and sintered at a maximum of 1300°C for 7 hours, resulting in a sintered product with a sintered density of 98% and a very good structure. was gotten.

As a result of analyzing the carbon content of the sintered product, as shown in Table 1, it was as low as 0.014 wt%, and the oxygen content was 0.059-t.
% had decreased significantly.

When this sintered product was tested for corrosion resistance, it showed good results without rusting in both the salt spray test and the artificial sweat test.

〔Effect of the invention〕

As shown in Table 1 showing Example 1.2 and Comparative Examples 1 to 3 above, according to the present invention, carbon contained on the surface and inside of the powder is removed during sintering, resulting in a sintered density It exhibits many effects, such as improved hardness, significant inclusions and pinholes, and good &llr& properties, making it possible to obtain sintered parts with excellent corrosion resistance and polished appearance.

that's all Applicant: Seiko Electronic Components Co., Ltd. Agent: Patent Attorney Takayoshi Hayashi

Claims (2)

[Claims] (1) In the stainless steel powder for sintering, which is the starting material for the method of manufacturing a sintered body in which stainless steel powder is mixed with a binder, injection molded, the binder is degreased, and then sintered, the remaining after degreasing Stainless steel powder for sintering that contains oxygen in an amount commensurate with the reaction in order to remove residual carbon through the C+O→CO reaction during sintering. (2) The stainless steel powder for sintering according to claim 1, wherein the amount of oxygen present in the powder is 0.8 wt% to 1.0 wt%.